Hurricane Series: Stormwater

View of Hurricane stormwater damage on 701.
on 12 August 2020
  • hurricane season
  • stormwater
  • damage

In the first blog entry for our hurricane series, I focused on the impacts of debris from a storm. If you missed it or happened to love it so much you want to read it again, you can find it here: Hurricane Series: Debris Monitoring Blog

For our second entry, I’m going to shift the focus to something even more dangerous: stormwater. You might be thinking, there is no way a few inches of rain is more dangerous than your lawn chair flying at 80 mph. Well, I can tell you, it is. Even an average strength hurricane can drop about nine inches of rainfall on any given area in its path. This can cause widespread flooding, damage to critical infrastructure and far-reaching environmental problems. Let’s see your missing lawn chair do any of that.


FLOOD DAMAGE

We have all seen the devastation in the news that occurred from flooding because of the hurricanes that have struck the United States and Puerto Rico. Some areas are still feeling the impacts from hurricanes such as Harvey, Maria, Irma and Michael which all made landfall two or more years ago; and everyone remembers how long the devastation lasted in New Orleans after Hurricane Katrina.


Chart showing the top 10 costliest hurricanes.

List of Costliest Atlantic Hurricanes // Wikipedia Reference: https://en.wikipedia.org/wiki/List_of_costliest_Atlantic_hurricanes

According to the CDC, flooding is the leading cause of death from hazards relating to storms. What can be done to help alleviate the impacts of flooding? Engineers can easily design storm drainage systems which make the impacts of average rainfall and thunderstorms negligible, but hurricanes aren’t your average thunderstorm. Unfortunately, our existing drainage systems can become overwhelmed by hurricane rainfall. Without an unlimited budget to completely change the lay of the land of an area, we can’t eliminate the build up of water in low-elevation areas and wetlands.

That doesn’t mean we can’t always keep improving though! Here are a few strategies engineers implement to mitigate the risk of flooding:

  • Introduce permeable pavements that absorb water and reduce runoff.
  • Complete more complex drainage studies for problem areas.
  • Regulate development in upland areas.
  • Enforce Low Impact Development techniques.
  • Plant more trees and vegetative buffers.
  • Require pavement to follow land contours.

All of the above are great small steps engineers are taking to keep us safe from hurricanes. None of these are end-all be-all perfect solutions for flooding, but just like rain is never going to stop falling, engineers are never going to stop solving the problems it creates.


INFRASTRUCTURE DAMAGE

Another impact stormwater has on our lives is the damage to our roadways and bridges. Water will always find its way, and sometimes it decides one of our bridges is in the middle of that way. This can cause bridges and culverts over streams and rivers to fracture from the surrounding land. To give you an idea of what this can look like, below is an image from before an emergency replacement our engineers worked on near Whiteville, N.C. after Hurricane Matthew in 2016. I don’t recommend trying to drive over that, but I’m not a structural engineer so take that with a grain of salt.


Image showing culvert damage on NC 701 near Whiteville, N.C.

Emergency replacement near Whiteville, N.C. after Hurricane Matthew in 2016


The keys for lowering the impact of this type of damage are prevention and a quick response to structure failure. The simplest and probably best strategy for preventing this type of damage is enforcing proper maintenance protocols. Engineers can monitor erosion of the surrounding soil, corrosion of foundations and damage caused by debris. The small bridges and culverts over streams are at the biggest risk for this type of damage. Thankfully most if not all states in the southeast have a low impact bridge replacement program which replaces deficient structures before they can become a problem.

However, mother nature doesn’t care very much about our good intentions to replace defective bridges and can take them down before we get the chance. In this event, it’s good to have a contingency plan. The culvert destroyed by Hurricane Matthew above is a great example of a quick response by the state and an engineering team. Matthew was making landfall in early October of 2016, and the state was procuring engineering services to replace it within 2 weeks. The engineering team conducted a review and noted the severe scour that allowed the culvert to settle and sever the roadway. In the design phase, the team determined the best solution was a replacement bridge, and construction was completed as early as possible. This fast response is the ideal situation for severe structural damage, but it isn’t always this smooth. Sometimes it’s just out of anyone’s control. Dangerous site conditions after the fact can delay response to getting our roads and bridges safe. It might seem like a slow and agonizing process getting the bridge replaced on your fastest route to work, but everyone is truly working as fast as possible to get it up and running again!


ENVIRONMENTAL DAMAGE

The stormwater runoff from a hurricane comes with a great risk to our environment as well. The damage caused by this is a literal slippery slope. When water is running off roadways and structures, it will accumulate pollutants such as insecticides, oils, trash, sediment, and human and animal waste. This contaminated stormwater can then flow into existing water sources such as rivers, lakes and aquifers. These hazardous substances can pollute the water we drink and use daily, clog streams, spread disease and destroy local ecosystems. That is a lot of damage all because of some extra rain.


Hurricane flooding in Franklin Virginia

Flooding in the city of Franklin, Virginia after Hurricane Floyd


Even though engineers are constantly evolving the latest stormwater runoff practices, a large cause of stormwater pollution on a regular basis is our daily activity. Thankfully, you don’t have to be an engineer to help with these environmental impacts of a hurricane! The Environmental Protection Agency suggests taking these steps to reduce stormwater pollution:

  • Don't dump waste into storm drains.
  • Keep yard clippings out of the street.
  • Dispose of household chemicals properly by following the directions on the package or by calling the local public works department for proper disposal guidelines.
  • Clean up oil spills and fix leaking automobiles.
  • Use drip pans to catch engine oil and other pollutants while repairing cars.
  • Recycle used motor oil.
  • Sweep driveways clean instead of hosing them down.
  • Wash your car at a commercial car wash, or at least wash your car on an unpaved surface so the excess water can be absorbed by the ground.
  • Drain swimming pools and spas into a sanitary sewer outlet, never into a street. Check first with your local wastewater treatment plant before disposing of anything in the sewer.

The havoc inflicted by stormwater is scary, but it’s scarier knowing it’s a problem we can never fully eradicate. Our society has come a long way with mitigating the effects of stormwater, and only continues to get better as we progress. Take pride in knowing that even though stormwater is the most dangerous side effect of a hurricane, we can all pitch in to help each other with it. So get out there and thank a civil engineer, wash your car on the grass and pull that lawn chair out of your neighbor’s pool.